And on Tuesday evening at approximately 11:26 p.m. ET, part of that mission came to an end.

After spending a record-breaking 340 days in space — longer than any American before him — Kelly arrived safely back on Earth, packed inside a snug Soyuz capsule with cosmonauts Sergey Aleksandrovich Volkov and Mikhail Korniyenko, who also just completed 340 days in space.

Kelly's trip back to solid ground marks an end to his epic life in space. Now the real work begins.

Sending an astronaut into space to live for nearly a year on the ISS is one of the most ambitious missions NASA has ever launched in its efforts to eventually send humans to Mars.

See photos of Kelly's return to Earth:

18PHOTOS

Astronaut Scott Kelly returns to Earth

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An extreme astronaut just returned safely to Earth -- and scientists can't wait to see him

Members of NASA support team help International Space Station (ISS) crew member Scott Kelly of the U.S. to get off a helicopter on arrival from the landing site at the airport of the town of Dzhezkazgan, Kazakhstan, on March 2, 2016. US astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko returned to Earth on March 2 after spending almost a year in space in a ground-breaking experiment foreshadowing a potential manned mission to Mars. AFP PHOTO / POOL / KIRILL KUDRYAVTSEV / AFP / POOL / KIRILL KUDRYAVTSEV (Photo credit should read KIRILL KUDRYAVTSEV/AFP/Getty Images)

Expedition 46 Commander Scott Kelly of NASA rests in a chair outside of the Soyuz TMA-18M spacecraft just minutes after he and Russian cosmonauts Mikhail Kornienko and Sergey Volkov of Roscosmos landed in a remote area near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)

International Space Station (ISS) crew member Scott Kelly of the U.S. shows a victory sign after landing near the town of Dzhezkazgan, Kazakhstan, on March 2, 2016. US astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko returned to Earth on March 2 after spending almost a year in space in a ground-breaking experiment foreshadowing a potential manned mission to Mars. AFP PHOTO / POOL / KIRILL KUDRYAVTSEV / AFP / POOL / KIRILL KUDRYAVTSEV (Photo credit should read KIRILL KUDRYAVTSEV/AFP/Getty Images)

Russian cosmonauts Mikhail Kornienko, left, Sergey Volkov of Roscosmos, center, and Expedition 46 Commander Scott Kelly of NASA, rest in chairs outside of the Soyuz TMA-18M spacecraft just minutes after they landed in a remote area near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)

Russian cosmonaut Mikhail Kornienko of Roscosmos is carried into a medical tent after he and Expedition 46 Commander Scott Kelly of NASA and Russian cosmonaut Sergey Volkov landed in their Soyuz TMA-18M spacecraft in a remote area near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)

Expedition 46 Commander Scott Kelly of NASA rests in a chair outside of the Soyuz TMA-18M spacecraft just minutes after he and Russian cosmonauts Mikhail Kornienko and Sergey Volkov of Roscosmos landed in a remote area near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)

Russian cosmonaut Sergey Volkov of Roscosmos is carried into a medical tent after he and Expedition 46 Commander Scott Kelly of NASA and cosmonaut Mikhail Kornienko landed in a remote area near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)

International Space Station (ISS) crew member Scott Kelly of the U.S. reacts after landing near the town of Dzhezkazgan, Kazakhstan, on March 2, 2016. US astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko returned to Earth on March 2 after spending almost a year in space in a ground-breaking experiment foreshadowing a potential manned mission to Mars. AFP PHOTO / POOL / KIRILL KUDRYAVTSEV / AFP / POOL / KIRILL KUDRYAVTSEV (Photo credit should read KIRILL KUDRYAVTSEV/AFP/Getty Images)

Russian cosmonaut Mikhail Kornienko of Roscosmos rests in a chair outside of the Soyuz TMA-18M spacecraft just minutes after he and Expedition 46 Commander Scott Kelly of NASA and Russian cosmonaut Sergey Volkov landed in a remote area near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)

A search and rescue team works at the site of landing of the Soyuz TMA-18M space capsule near the town of Dzhezkazgan, Kazakhstan, on March 2, 2016. US astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko returned to Earth on March 2 after spending almost a year in space in a ground-breaking experiment foreshadowing a potential manned mission to Mars. AFP PHOTO / POOL / KIRILL KUDRYAVTSEV / AFP / POOL / KIRILL KUDRYAVTSEV (Photo credit should read KIRILL KUDRYAVTSEV/AFP/Getty Images)

Russias Soyuz TMA-18M space capsule carrying the International Space Station (ISS) crew of US astronaut Scott Kelly and Russian cosmonauts Mikhail Kornienko and Sergei Volkov lands in a remote area outside the town of Dzhezkazgan, Kazakhstan, on March 2, 2016. US astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko returned to Earth on March 2 after spending almost a year in space in a ground-breaking experiment foreshadowing a potential manned mission to Mars. AFP PHOTO / POOL / KIRILL KUDRYAVTSEV / AFP / POOL / KIRILL KUDRYAVTSEV (Photo credit should read KIRILL KUDRYAVTSEV/AFP/Getty Images)

The Soyuz TMA-18M spacecraft is seen as it lands with Expedition 46 Commander Scott Kelly of NASA and Russian cosmonauts Mikhail Kornienko and Sergey Volkov of Roscosmos near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)

The Soyuz TMA-18M spacecraft is seen as it lands with Expedition 46 Commander Scott Kelly of NASA and Russian cosmonauts Mikhail Kornienko and Sergey Volkov of Roscosmos near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)

NASA astronaut Scott Kelly hugs his crewmates goodbye on the International Space Station on March 1, 2016. Photo credit: NASA

NASA astronaut Scott Kelly with his crewmates on the International Space Station on March 1, 2016. Photo credit: NASA

NASA astronaut Scott Kelly hugs his crewmates goodbye on the International Space Station on March 1, 2016. Photo credit: NASA

NASA astronaut Scott Kelly hugs his crewmates goodbye on the International Space Station on March 1, 2016. Photo credit: NASA

NASA astronaut Scott Kelly hugs his crewmates goodbye on the International Space Station on March 1, 2016. Photo credit: NASA

But there are many questions that need answers before NASA is ready for the red planet.

Now that Kelly is back on Earth, scientists can begin to answer some of those questions. They'll start by analyzing, in detail, how Kelly's 340-day stay in space has affected his body.

Life in space

Pete Souza - Official White House Photo by Pete Souza via NASA

Unfortunately, one of the most entertaining aspects about space is also the most harmful to the human body: microgravity.

Somersaulting in mid-air looks like great fun, but over time microgravity has a bizarre and potentially dangerous impact on physical performance.

For example, astronauts in the past have experienced impaired vision, changes in their sense of taste, and an increased flow of fluid to the brain.

Increased fluid flow to the brain is particularly concerning because when astronauts return to Earth, their blood pressure must readjust to Earth's gravity. But this takes time, and as a result some astronauts who have just returned can't stand up for more than 10 minutes without fainting.

Other concerns about long-duration spaceflight include a loss of bone and muscle mass, weakened immune system, and fatigue.

Kelly conducted a number of experiments during his time in space to help address these concerns, but now that he's back scientists can get a closer look at him.

They'll also observe how quickly he recovers. Recovery rate is important in predicting how much future astronauts — who land on Mars for brief periods — will be capable of doing, both physically and mentally, after spending 8.5 months in space, about the time it takes to get to Mars.

Take a look back at Scott Kelly's historic #YearInSpace from the beginning by clicking through the gallery below.

74PHOTOS

Scott Kelly's best photos from #YearinSpace

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An extreme astronaut just returned safely to Earth -- and scientists can't wait to see him

NASA astronaut Scott Kelly (@StationCDRKelly) captured this photograph of the green lights of the aurora from the International Space Station on Oct. 7, 2015. Sharing with his social media followers, Kelly wrote, "The daily morning dose of #aurora to help wake you up. #GoodMorning from @Space_Station! #YearInSpace"

October 10, 2015

Scott Kelly ‏(@StationCDRKelly): "#EarthArt In 377 cumulative days in space, I've never seen this before today. #YearInSpace"

October 12, 2015

Scott Kelly (‏@StationCDRKelly): "#EarthArt A single pass over the #Australian continent. Picture 10 of 17. #YearInSpace"

October 12, 2015

Scott Kelly (‏@StationCDRKelly): "#EarthArt in one pass over the #Australian continent. Picture 2 of 17. #YearInSpace"

October 13, 2015

Scott Kelly (‏@StationCDRKelly): "#EarthArt A single pass over the #Australian continent. Picture 15 of 17. #YearInSpace"

On Oct. 12-13, 2015, NASA astronaut Scott Kelly shared a series of seventeen photographs taken from the International Space Station during a flyover of Australia. This first photo of the series was shared on Twitter with the caption, "#EarthArt in one pass over the #Australian continent. Picture 1 of 17. #YearInSpace". (Photo via NASA)

This flowering crop experiment began on Nov. 16, 2015, when NASA astronaut Kjell Lindgren activated the Veggie system and its rooting "pillows" containing zinnia seeds. The challenging process of growing the zinnias provided an exceptional opportunity for scientists back on Earth to better understand how plants grow in microgravity, and for astronauts to practice doing what they’ll be tasked with on a deep space mission: autonomous gardening. In late December, Kelly found that the plants "weren't looking too good," and told the ground team, “You know, I think if we’re going to Mars, and we were growing stuff, we would be responsible for deciding when the stuff needed water. Kind of like in my backyard, I look at it and say ‘Oh, maybe I should water the grass today.’ I think this is how this should be handled.”

The Veggie team on Earth created what was dubbed “The Zinnia Care Guide for the On-Orbit Gardener,” and gave basic guidelines for care while putting judgment capabilities into the hands of the astronaut who had the plants right in front of him. Rather than pages and pages of detailed procedures that most science operations follow, the care guide was a one-page, streamlined resource to support Kelly as an autonomous gardener. Soon, the flowers were on the rebound, and on Jan. 12, pictures showed the first peeks of petals beginning to sprout on a few buds.

NASA astronaut Scott Kelly and ESA astronaut Tim Peake shared a series of aurora photographs taken from the International Space Station on Jan. 20, 2016. Kelly (@StationCDRKelly) wrote, "#goodmorning #aurora and the Pacific Northwest! #YearInSpace" and Peake (@astro_timpeake) followed up with, "Getting a photo masterclass from @StationCDRKelly – magical #aurora"

The dancing lights of the aurora provide spectacular views on the ground, but also capture the imagination of scientists who study incoming energy and particles from the sun. Aurora are one effect of such energetic particles, which can speed out from the sun both in a steady stream called the solar wind and due to giant eruptions known as coronal mass ejections or CMEs.

(Photo via ESA/NASA)

January 21, 2016

Astronaut Scott Kelly showed the world one of the unusual benefits of microgravity for astronauts living on board the International Space Station - liquid ping pong. NASA released video on Jan. 21 showing Kelly using a set of hydrophobic paddles and a ball of water and playing ping pong in space. (Photo via NASA)